1. Field of the Invention
This invention relates to a control apparatus and method for an automatic transmission mounted in an automobile or the like. More specifically, this invention relates to a method for determining timing to start torque-restore control.
2. Description of the Related Art
FIG. 3 is a block diagram showing the arrangement of apparatuses and their general relationships with respect to control of a typical engine and automatic transmission. Because this drawing has also been applied to a related example, it will be used to describe control of an engine 10 and an automatic transmission 12 in a vehicle, which is disclosed in JPA 2-308934. An ECU (electronic control unit) 14 controls the operation of various valves and plugs and the like in the engine 10 while monitoring the rpm and the like of the engine 10 using various sensors provided therein. A transmission control apparatus 16 controls a clutch and the like provided in the automatic transmission while monitoring the rotational speed and the like of an input shaft from the engine 10 to the automatic transmission 12 using various sensors provided in the automatic transmission 12. Further, the ECU 14 and the transmission control apparatus 16 work in coordination to execute typical torque-down control during shifting and torque-restore control following that shift.
Torque-down control in this case is control which is executed during a shift to reduce shift shock and extend the life of frictional engagement elements. This control temporarily reduces the torque output by the engine 10, i.e., engine torque, by a predetermined amount. At the same time that this control starts, the automatic transmission moves into an inertia phase and the rotational speed of the input shaft of the automatic transmission 12 gradually slows and approaches the speed that it needs to be for synchronization when the shift ends, i.e., approaches a shift-end synchronous speed. Ideally, it is preferable that the point at which a predetermined target time, i.e., a target inertia phase time, has elapsed from the start of the torque-down control, i.e., from the start of the inertia phase, be made the shift-end point, and that the rotational speed of the input shaft of the automatic transmission 12 at that shift-end point substantially match the target speed for the shift-end synchronous speed. Also, it is necessary that the engine torque, which has been reduced by the torque-down control, be returned to the value that it was before that torque-down control at the end of the shift. Therefore, torque-restore control which gradually increases the engine torque up to the value that it was before the start of the torque-down control is started at an appropriate point in the inertia phase.
The technology in JPA2-308934, however, estimates and detects a degree of change in the shift based on the difference between the current speed of rotating members inside the automatic transmission and the speed of those members at the end of the shift, and, based on those results, adaptively adjusts the amount of change of the engine torque in the torque-restore control. Detection of the degree of change in the shift is done using a map created with consideration given to various numerical values and quantities of state, such as the engine throttle opening amount, engine speed, and gear speed of the automatic transmission. Creating this map requires a tremendous number of man-hours.